1. Field of the Invention
The present invention relates to a pixel and an organic light emitting display device using the same, and more particularly, to a pixel for displaying an image with uniform brightness and an organic light emitting display device using the same.
2. Discussion of Related Art
FIG. 1 is a circuit diagram illustrating a pixel of a conventional organic light emitting display device. The pixel 4 of the conventional organic light emitting display device includes a pixel circuit 2 coupled to an organic light emitting diode (OLED), a data line Dm, and a scan line Sn. The pixel circuit 2 controls the OLED. A first power source ELVDD and a second power source ELVSS are coupled to the pixel 4.
An anode electrode of the OLED is coupled to the pixel circuit 2 and a cathode electrode of the OLED is coupled to the second power source ELVSS. The OLED generates light with brightness corresponding to the current supplied by the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the OLED in response to a data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn. In order to perform this operation, the pixel circuit 2 includes a first transistor M1, a second transistor M2, and a storage capacitor Cst. The second transistor M2 is coupled between the first power source ELVDD and the OLED. The first transistor M1 is coupled to the second transistor M2, the data line Dm, and the scan line Sn. The storage capacitor Cst is coupled between a gate electrode and a first electrode of the second transistor M2.
A gate electrode of the first transistor M1 is coupled to the scan line Sn and a first terminal of the first transistor M1 is coupled to the data line Dm. A second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst. One of the electrodes of each of the first and second transistors M1, M2 is set as a source electrode and the other electrode is set as a drain electrode. For example, when the first electrode is set as the source electrode, the second electrode is set as the drain electrode. When the scan signal is supplied by the scan line Sn, the first transistor M1 is turned on to supply the data signal supplied by the data line Dm to the storage capacitor Cst. As a result, a voltage corresponding to the data signal is charged in the storage capacitor Cst.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst and the first electrode of the second transistor M2 is coupled to the other terminal of the storage capacitor Cst and the first power source ELVDD. The second electrode of the second transistor M2 is coupled to the anode electrode of the OLED. The second transistor M2 controls the amount of current that flows from the first power source ELVDD to the OLED to correspond to the voltage value stored in the storage capacitor Cst. The OLED generates light with the brightness corresponding to the amount of current supplied by the second transistor M2.
However, according to the above-described conventional pixel 4, it may not be possible to display an image with uniform brightness. To be specific, the threshold voltages of the second transistors M2 included in different pixels 4 vary due to deviations introduced during the fabrication processes. When the threshold voltages of the second transistors M2 are not uniform, although data signals corresponding to the same gray level are supplied to a number of pixels 4, light components with different brightness are generated by the OLEDs of each pixel 4. The difference in brightness is due to the difference between the threshold voltages of the second transistors M2 of each pixel.